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تسجيل مستخدم جديدRobust s+/- pairing in CaK[Fe(1-x)Ni(x)]4As4$ (x = 0 and 0.05) from the response to electron irradiation
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Controlled point-like disorder introduced by 2.5 MeV electron irradiation was used to probe the superconducting state of single crystals of CaKx superconductor at $x = 0$ and 0.05 doping levels. Both compositions show an increase of the residual resistivity and a decrease of the superconducting transition temperature, $T_c$ at the rate of $dT_c/drho(T_c) approx$ 0.19 K(textmu$Omega$cm)$^{-1}$ for $x=0$ and 0.38 K(textmu$Omega$cm)$^{-1}$ for $x=:$0.05, respectively. In Ni - doped, $x = 0.05$, compound the coexisting spin-vortex crystal (SVC) magnetic phase is suppressed at the rate of $dT_N/drho(T_N)approx$ 0.16 K(textmu$Omega$cm)$^{-1}$. Low - temperature variation of London penetration depth is well approximated by the power law, $Delta lambda (T) = AT^n$ with $napprox,$2.5 for $x=0$ and $napprox,$1.9 for $x=0.05$ in the pristine state. Electron irradiation leads to the exponent $n$ increase above 2 in $x=0.05$ suggesting superconducting gap with significant anisotropy that is smeared by the disorder scattering. Detailed analysis of $lambda (T)$ and (T_{c}) evolution with disorder is consistent with two effective nodeless superconducting energy gaps due to robust s$_{pm}$ pairing. Overall the behavior of CaKx at $x = 0$ is similar to a slightly overdoped BaK at $y approx$ 0.5 and at $x= 0.05$ to an underdoped composition at $y approx$ 0.2.
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